Persson, Henrik

Abstract [en]

The purpose of this thesis was to analyse and develop a method for selecting the mounting position of a sensor cluster used in vehicles. The sensor cluster is a collection of sensors, measuring linear acceleration and rotational speed in 3 dimensions x-y-z. Other functions (such as the ESP-system) rely on the input data measured by this sensor cluster and it is supposed to describe the acceleration and speed of the vehicle’s Centre of Gravity (COG). It is not always a convenient mounting position to mount the DCU in COG. When positioning it at any other place in the vehicle the measured data for rotational speed will deviate though and ideal it’s just a transformation to COG. Measurement errors will appear though (they always do), and these are mapped non-linearly to COG. How this transformation and mapping of errors looks like, is analysed in the report. The theory for an ideal transformation is derived (rotational mechanic and dynamic equations) and the error types that have to be considered are determined and said to be offset, sensitivity, drift, peak- and noise errors. The error types offset, sensitivity and drift have been described theoretically as substitutions of the measured values, e.g. measure + instead of just measure. By doing this for the mentioned error types, an error matrix describing only the amplification effects for the specified errors is found. A similar theoretical substitution also for noise is derived, but because of the random and irregular structure of noise, the output is not as black or white as for the other error types. The error matrix is a key part in the multiplication with the mounting position vector where the result describes how big the error is for a chosen mounting position. By switching the variables solved for, and instead specifying that errors within a, b and c units big are allowed, valid mounting positions in a 3D space are found. The last step of describing the 3D-space has been calculated in two different ways. Either by testing every mounting position in a certain range and transform to COG: is the transformed error too big or not? The other solution is testing the positions on a 2D plane, and calculates: how big deviation can be accepted for the specified size of error? Not always any valid position outside COG is found, and then the allowed size of errors might have to be changed or better equipment has to be used. To make use of the theory and equations that have been developed, a Graphical User Interface has been programmed in Matlab 7 SP2. In the GUI the error types can be chosen and by manually enter manoeuvre data or by loading measurement data from file, the allowed mounting positions in 3D are calculated. To conclude, the thesis has worked out well and the goals of the project have been reached.